seq_file: disallow extremely large seq buffer allocations

There is no reasonable need for a buffer larger than this, and it avoids
int overflow pitfalls.

Fixes: 058504e ("fs/seq_file: fallback to vmalloc allocation")
Suggested-by: Al Viro <[email protected]>
Reported-by: Qualys Security Advisory <[email protected]>
Signed-off-by: Eric Sandeen <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: Eric Sandeen

fs/seq_file.c

@@ -32,6 +32,9 @@ static void seq_set_overflow(struct seq_file *m)
 
 static void *seq_buf_alloc(unsigned long size)
 {
+	if (unlikely(size > MAX_RW_COUNT))
+		return NULL;
+
 	return kvmalloc(size, GFP_KERNEL_ACCOUNT);
 }